Exposure time

sample displays of exposure time by digital cameras

Exposure time or shutter speed is the time during which light falls onto the image sensor of a digital camera.

It is measured in seconds and fractions of a second may be displayed as reciprocals, so e.g. 125 for 1 ∕ 125 = 125th of a second.

On the left are some samples how the exposure time appears on the monitor of a compact camera, two DSLR cameras and the LCD display of a DSLR.

display of whole second exposure time by digital cameraWhole seconds get the symbol ʺ, so e.g. 1ʺ is displayed for one second.

Exposure times are organized in exposure values, so by multiplying and dividing with two repeatedly. The resulting series of exposure time is slightly rounded to get figures that are easier to remember (but cameras use internally the exact, slightly different values):

4 ʺ
2 ʺ
1 ʺ
1 ⁄ 2
1 ⁄ 4
1 ⁄ 8
1 ⁄ 15
1 ⁄ 30
1 ⁄ 60
1 ⁄ 125
1 ⁄ 250
1 ⁄ 500
1 ⁄ 1000

This list of exposure times in steps of full exposure values is commonly used since decades. Cameras use additional intermediate values for higher precision.